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<span class="card-header">
<h2>Antenna Consutrction and Design: HF Antennas</h2>
</span>
</button>
<div class="container content; display: show">
<h2>Radio</h2>
<h5>- - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -</h5>
<p>
In 2020, I attained an amateur radio station license (callsign, KO4DNM) and soon after, upgraded to the
General class license.
In this time, I found myself deeply interested in antenna design and construction, and constructed a number
of antennas,
each resonant at the different amateur radio station frequency bands.
These frequency ranges lie within the HF spectrum, between 1.8Mhz and 29Mhz. I focused largely on the ~14MHz
region (20M Band)
during the day time, and lower frequencies at night (~7MHz, the 40M Band, was one of my favorites).
Propagation was often nicely
split in this manner, with optimal long-distance contact best on the higher frequencies during the light
hours, with a sometimes-sudden
shift to optimal performance on the lower frequencies as the sun set.
During this time, I made over 700 logged radio contacts, including at least one person from each continent,
and nearly 100 different
countries. More info on this can be found on my QRZ and HRDLog profiles.
To produce these results, I had to create a robust plan including details as simple as how many feet of
coaxial cable I would need
to cut, to much more complicated design of the antennas themselves. My plan included some of the following
elements:</p>
<p> Step 1: Location Planning: Determine optimal location for antennas as well as optimal antenna type; I
settled on a multi-element
dipole (also called a "fan dipole" for the lower frequencies, and a hex-beam antenna for the higher
frequencies)</p>
<p>Step 2: Antenna Design: Complete antenna design (using MMANA-GAL)</p>
<p>Step 3: Feed Line: Determine sufficient quantity of coax, as well as high quality RF connectors</p>
<p>Step 4: Logistics: Acquire necessary materials for antenna (copper wire for antenna elements, proper-type
toroidal cores for baluns)</p>
<p>Step 5: Construction of the antennas, Phase I: Wire Elements: For the dipole, this meant measuring out the
elements to their resonant lengths,
while also taking into account an increase in velocity due to the rubber coating, which resulted in lowering
of the resonant frequency by a small,
but significant degree. For the hexbeam antenna, I ultimately ended up purchasing a used frame in which I
cut new wire elements for.</p>
<p>Step 6: Construction, Phase II: Baluns / Chokes: Due to the imperfect feed-point impedance of antennas in the
real world, especially a wire
dipole used on a wide range of frequencies, I decided to implement a balun for the dipole antenna, and a
common mode choke (or 1:1 balun)
for the hexbeam (as the hexbeam is configured to be resonant at all desired frequencies)</p>
<div class="card paragraph" style="margin: auto; text-align: center">
<img src="category_photos/Screenshot%20from%202022-02-19%2020-12-31.png"
alt="choke balun, common mode choke, jeremy laratro">
<img src="/img/20201112_183254.jpg" style="width: 30vw;" alt="antenna, HF, radio, jeremy laratro">
</div>
<p> Step 7: Verification: At this point, everything was built and ready for implementation, and I double-checked
all element lengths as well as any
connections I made when constructing the balun and isntalling the PL-259 RF connectors on the RF400
coax.</p>
<p>Step 8: Implementation: I decided to implement the antennas in "stages", and installed the hexbeam antenna
first. After a few weeks,
the dipole was also installed.</p>
<p>Step 9: Testing: After installing the antennas, I performed a wide array of different tests to ensure that I
was achieving optimal power
transfer between the 100w output of my HF radio and the antenna elements. One of my favorite methods of
testing antennas and RF circuits
in general is with a VNA, and thanks to the open-source NanoVNA, I, as an independent entity can afford an
instrument like a VNA which would
otherwise cost upwards of $3000. I also performed SWR tests, as well as TDR tests. I was able to acquire a
used Tektronix TDR analyzer,
which is great for analyzing feed lines for any shorts, opens, or other issues.</p>
<p>Step 10: The last step of the plan, which is to use and enjoy the antennas. These two antennas have been used
to achieve communications,
both voice and digital protocols, with people in nearly 100 countries and every continent, including
Australia, New Zealand, Japan,
and many more. I have experimented with a large number of different communications protocols ranging
from:</p>
<p>Single side-band(SSB): USB/LSB</p>
<p>Phase shift keying (PSK): PSK-31</p>
<p>Digital voice: FreeDV</p>
<p>Multiple frequency-shift keying (MFSK): OLIVIA, JT65, FT4, FT8 (two of various incredible weak-signal mode
created by astrophysicist Joe Taylor (K1JT)</p>
<p>Frequency shift keying (FSK): RTTY (Radio teletype)
<p>Hellschreiber</p>
<h5>- - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -</h5>
<div class="card paragraph" style="margin: auto;text-align: center;">
<img src="/img/20200830_162401.jpg" style="width: 30vw;" alt="antenna, HF, radio, jeremy laratro">
<p>Above: 6-Band hexbeam antenna that I also installed. In order to take advantage of directional effects, I
mounted this antenna on a tripod,
connected to a TV antenna rotator which I routed underground and then through my window using a
custom-built pass-through with PL-259 connections</p>
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